1. Field of the Invention
The present invention relates to a sound signal adjustment apparatus and method and a telephone such as a portable telephone.
2. Description of the Related Art
By their nature, portable telephones are used under a wide variety of ambient conditions, frequently outdoors. Often they are used in speaking and listening environments that are inferior to the environments in which landline outdoor telephones are used.
For example, portable telephones are usually used in an exposed environment, rather than an enclosed environment such as a telephone booth. The voices of both parties in the telephone conversation may therefore become hard to hear because of ambient noise. The user can cope with this situation by turning up the volume of the telephone set.
Because of the primary need for portability, however, portable telephones have become extremely small. The buttons and other manual controls of a modern portable telephone are crowded into a small space on the front and sides of the telephone body.
This leads to volume control problems, because often the user of a portable telephone does not realize that the volume setting of the telephone's speaker is too low until after the conversation has begun. To adjust the volume to the proper level, the user must operate the manual volume control, but with today's downsized telephones it is difficult to find the volume control by touch alone. With the increasing number of functions being built into modern portable phones, there is also the risk of operating the wrong control by mistake and activating an unintended function. To adjust the volume, the user must therefore take the telephone away from his or her head so that he or she can see where the volume control is and how to operate it. While the user is adjusting the volume, the distant party, unless warned in advance, will assume that the user is still listening and will continue to talk. The user will accordingly miss part of what the distant party says.
To make matters worse, the distant party may become aware that the user has missed part of the conversation without being aware that this occurred because the user was turning up the volume. The distant party may suspect that the user simply was not paying attention or had lost interest in the conversation, resulting in damage to personal relations between the two parties.
To avoid such problems, Japanese Patent Application Publication (JP) 2005-20730 discloses a portable telephone having a pressure sensor embedded near the speaker to measure mechanical pressure, enabling the user to adjust the volume just by pressing the telephone more or less tightly against his or her ear, without operating any manual controls.
JP H01-241208 discloses terminal equipment with a speaker and a microphone. The equipment uses the microphone to detect the magnitude of ambient noise, and increases the speaker volume in noisy environments.
JP H07-038624 discloses a telephone that has a sensor for sensing the sound pressure in the enclosed space between the earpiece of the handset and the user's ear, and adjusts the earpiece speaker volume accordingly. When the earpiece is pressed tightly against the ear, causing the sound pressure to rise, the volume is reduced; when the earpiece is held only loosely against the ear, causing the sound pressure to fall, the volume is increased.
JP H11-284694 discloses a portable telephone that adjusts its speaker volume according to the volume of the user's voice as picked up by the microphone. When the user raises his or her voice, the speaker volume is increased.
JP 2008-187221 discloses a portable telephone with a camera mounted on the same surface as the telephone's display screen. The image captured by this camera is analyzed; if the number of black picture elements in the image is equal to or greater than a threshold value, indicating that the telephone is being held against the ear, the distant party's voice is output through an ear speaker; otherwise, the distant party's voice is output through a separate hands-free speaker integrated into the telephone body.
JP 2007-116585 discloses a noise canceling device for a conference system with multiple microphones. The device cancels noise by spectral subtraction, subtracting a stored noise pattern corresponding to a selected microphone.
In the context of today's portable telephones, all of the above disclosures are problematic.
One reason is the ever-decreasing size and increasing functionality of portable telephones, noted above. The increasing functionality demands an increasing number of buttons and other manual controls. The decreasing size leaves little room for additional sensors. For example, it is difficult to find space in which to embed the pressure sensor required by JP 2005-20730.
The method disclosed in JP H01-241208 of controlling speaker volume according to the ambient noise level detected by a microphone could in theory be applied to a portable telephone to adjust the speaker volume without requiring an additional sensor, but this method fails to meet all the requirements of a portable telephone. For example, it fails when the user wants to increase the speaker volume, not because of ambient noise, but because the distant party is speaking in a small voice.
JP H07-038624 requires an additional sound pressure sensor, and in any case is inapplicable to portable telephones which, differing from landline telephones, are rarely held tightly to the ear. A more basic problem is that if the user did press a portable telephone against his or her ear in order to hear the distant party's voice better, JP H07-038624 would respond by decreasing the speaker volume, making the distant party's voice even harder to hear.
JP H11-284694 enables the user to increase the speaker volume when desired, without using manual controls, just by raising his or her own voice. A problem is that the user may be using the portable telephone in a quiet environment and may want to increase the speaker volume because the distant party is talking in a small voice. In this case the user may hesitate to raise his or her own voice because that would disturb other people nearby. A more subtle problem is that, since the portable telephone does not distinguish between the user's voice and ambient noise, the speaker volume is automatically increased in response to ambient noise in a noisy environment. Since that makes the distant party's voice easier to hear, the user thinks that he or she does not need to raise his or her own voice and tends not to do so. As a result, the distant party has difficulty hearing the user's voice over the ambient noise.
A problem with JP 2008-187221 is that in almost all camera-equipped portable telephones, the camera is not mounted on the same surface as the display screen; it is mounted on the opposite surface and points away from the user's head. Even in portable telephones with two cameras, front and back, there is the problem that use in a dark environment can cause an unwanted switchover from the hands-free speaker to the ear speaker even though the telephone is distant from the user's head. Furthermore, this camera-based method only provides a way of switching from one speaker to another; it does not provide a method of adjusting the volume of a speaker.
A problem with the spectral subtraction method of JP 2007-116585 is that it does not work well when a microphone is carried from one location to another location with a different ambient noise pattern, a frequent occurrence with portable telephones.